The invention relates to a process for producing a printed circuit board with at least one conductor path applied as a metal layer on at least one electrically insulated surface of a substrate board, wherein the printed circuit board has connection areas for connection contacts. The invention also relates to a printed circuit board and uses therefor.
A measuring resistor for resistor thermometers is known from German Utility Model 80 03 431, which has a small ceramic board on which a thin resistance layer is applied. The lead-in wires necessary for electrical bonding are passed through borings of an insulating body and are melted onto the small ceramic board along with this resistance layer by means of a glass frit, whereby the resistance path is covered with a burned-in insulation layer of glass ceramic. The comparatively complex construction, which is hardly suited for a mass production of economical measuring resistors measuring resistors, proves to be problematic with the known arrangement.
Furthermore, from DE 30 02 112 A1, a paste with predetermined electrical conductivity is known in which an electrically non-conducting support material is provided with additives in order to attain a specified conductivity. Such a paste is used, for example, as a contact and solder mass for layer circuits in heating elements or sensors. It can be applied in usual processing procedures as, for example, screen printing.
In practice, such terminals applied in screen printing turn out to be suitable only for connection with thin wires and bonding wires or thin bands in a soft soldering process, owing to their slight layer thickness. When using standard connection wires, as are usual for cable connections, a poor mechanical fixation between connection wire or cable lead and the contact field on the substrate must be taken into consideration, from which a rapid separation can result, especially at elevated temperature or with mechanically high tensile stress. When using a thin bonding wire, this must then be lengthened further, from which difficulties can result in automated processes.
An object of the invention is to create a printed circuit board with a metallic conductor path in thin or thick layer technology with connection positions such that a typical connection contact of a connection lead can be directly plugged in, or a stranded wire can be directly hard soldered or directly welded on. The wire or stranded wire should, in addition, satisfy standard macroscopic connection technology, that is, be jacketed with desired insulation material, as for example fiberglass or silicone. Furthermore, usages of such a printed circuit board are provided.
The object is accomplished in accordance with the invention by a process including the steps of applying connection areas of a conductor path to a substrate having a ceramic surface, such that holes are formed in connection areas to expose areas of the substrate surface, applying active solder to the connection areas, subsequently applying a small contact plate to each connection area as a connection contact covering the active solder, and soldering the small contact plates to the conductor path and to the areas of the substrate surface exposed by the holes of the connection areas.
It also proves advantageous that the small contact plates provided for subsequent connection contacts be connected directly with the electrically insulated surface of the substrate through holes of connection areas, so that a firm connection results.
In a preferred embodiment of the process, the small contact plate is applied as a connection lug. Here the simple connectivity to a structural connection proves to be advantageous.
In a preferred configuration of the process, auxiliary and carrier strips for the metallic parts (contact plates) are removed by sawing, breaking and tearing off. Further advantageous configurations of the process are presented in dependent claims. The active solder may be applied as a paste, as a shaped solder part, or as a plated-on layer of a small contact plate. The solder may be applied as a dispensable material by means of a dosing facility.
It has proved advantageous, furthermore, to have the comparatively simple application of contact surfaces with a plurality of measurement elements in the form of a multi-unit panel on a continuous ceramic substrate in a single process step. Above and beyond this, a statistical quality control is possible in an especially simple manner, since all measuring resistors are contacted according to the same process.
The object is further accomplished in accordance with an arrangement for a printed circuit board wherein the connection areas of the conductor path have holes with exposed areas of a substrate having a ceramic surface, the connection areas and the areas of the substrate exposed by the holes being firmly connected electrically and mechanically by active solder to small contact plates applied as connection contacts using a protective gas or vacuum soldering process.
Simple external contacting proves to be advantageous, so that now standard connection wires or stranded wires can be directly hard soldered or welded with the contacts of the printed circuit board, from which a simple assembly and a high reliability result.
In a preferred embodiment, the small contact plates are made of a nickel or nickel-iron alloy, from which good temperature stability, good sweat solderability and a low contact resistance advantageously result.
The electrically insulating surface of the substrate preferably comprises aluminum oxide ceramic. The holes of the connection areas applied to the substrate surface are constructed in the form of window-shaped openings, so that a secure and stable connection between the ceramic, and the soldered-on contact plate arises. Advantageous configurations of the printed circuit board are presented in dependent claims.
The object is further accomplished in accordance with usage of the printed circuit board as a measuring resistor or heating element wherein the printed circuit board is constructed as a resistance, or usage for capacitance measurements wherein the printed circuit board is constructed as an electrode structure.
When using the printed circuit as a measuring resistor, the rapid response time proves to be particularly advantageous, since the conductor path as thin layer element contains only a low thermal inertia.
The conductor path is applied in an advantageous configuration as a thin layer or thin film of platinum group metals in a photolithographic process.